Development and genetic mechanism of complex carbonate reservoir fractures: A case from the Zanarol Oilfield, Kazakhstan

By core observation and slice analysis, two types of fractures can be identified in reservoirs of Zanarol Oilfield, including macro-fractures and micro-fractures. Macro-fractures refer to tectonic fractures and stylolites, and micro-fractures mainly refer to grain breakage fractures and micro-tectonic fractures. The development of the different scale fractures is controlled by lithology, formation texture and stress field. Macro-fractures are well developed in tight rocks such as micrite and micro-fractures are well developed in granular carbonate rocks of good porosity and permeability. The Zanarol Oilfield is a typical layered pool, with interbeds of granular carbonates and tight carbonates, and this texture controls the vertical distribution of macro-fractures and micro-fractures. Macro-fractures in the ? layer are well developed due to its tight reservoir, and micro-fractures are well developed in the ? layer because of its loose reservoir. The planar distribution of the fractures is controlled by principal stress, and fractures are well developed in zones with high principal stress.